(1) The way to interpret Gal. 3:27-29 is by viewing it with its "cognate" or parallel passages:
"For by one Spirit we were all baptized into one body--Jews and Greeks, slaves or free--and all were made to drink of one Spirit' (1 Cor. 12:13)
Paul isn't saying that practical differences are erased but rather that all may "drink of one Spirit" or as Kahn says, "[1 Cor. 12:13] does not suggest that the original distinctions are erased, only that all can access the sacred," [Emphasis added].
I like how he puts that.
(2) The Three Blessings in Jewish liturgy probably come from ancient Greek thought. And when I say "probably", the Rabbis basically borrowed this directly from the Greeks:
pg. 9 "In its best-known form, the statement was attributed to Socrates, who is reported to have said:
'[T]here were three blessings for which he was grateful to fortune:
First, that I was born a human being and not one of the brutes;
Next, that I was born a man and not a woman;
Thirdly, a Greek and not a barbarian.'"
pg. 10 "The earliest source for a parallel Jewish text to the Greek aphorism is in the Tosefta, the collection of early rabbinic texts attributed to teachers who lived before the year 200 CE. Tosefta Berakhot 6:18 reads: 'Rabbi Judah says: A person must bless three blessings every day: 'Praised [are You Eternal...] who did not make me a gentile, praised [...] who did not make me a boor, praised [...] who did not make me a woman.' A slightly different version is recorded in the Babylonian Talmud in Tractate Menahot."
pg. 12 "Several Palestianian-influenced liturgical texts preserve Jewish parallels identical to the Greek's 'affirmative and not negative' style. Although there were many variations circulating, the following arrangement found in a Genizah fragment is typical:
'Praised are You Eternal our God King of the Universe who
a person and not a beast
a man and not a woman
an Israelite and not a gentile
circumcised and not uncircumcised
free and not a slave.'
This example contains five paired identity statements...the Genizah text exactly mirrors the Greek version as recorded by Diogenes."
When we also factor in Rabbinic midrash like the following we see that the Three Blessings were formulated as "thank you for making me X [desirable thing] and not Y [undesirable thing]":
"9. Tosefta Berakhot 6:18...R. Judah says: Three benedictions a man is required to recite each day: Blessed [are You O Lord...] that You did not make me a Gentile. Blessed [are You O Lord...] that you did not make me an ignoramus. Blessed [are You O Lord...] that You did not make me a woman. A Gentile--as it is written, 'All the nations are as nothing before him; they are accounted by him as less than nothing and emptiness' (Isa 40:17)." (Parables of the Sages by Notley and Safrai)